This invention generally relates to motor control. More specifically, this invention relates to a method of estimating position information for a motor.
Electric motors typically are controlled to provide a desired performance. Position information regarding motor components is necessary to achieve accurate control. Various position determination techniques have been proposed.
One known technique of estimating motor component position involves superimposing a carrier voltage signal upon a fundamental control voltage signal and using a resulting carrier current signal from the motor to estimate a position of the rotor. A controller generates the fundamental control signal, which drives the motor rotor to produce rotational torque. The controller generates and superimposes the carrier voltage signal upon the fundamental control voltage signal in an open-loop fashion. The controller generates the carrier voltage signal at a consistent strength and at a relatively higher frequency than the fundamental control signal.
As the carrier voltage signal is a relatively high-frequency signal, the carrier voltage signal does not substantially affect the fundamental control signal driving the motor. This technique for estimating the angular position of the motor rotor is described in U.S. Pat. No. 5,585,709.
That technique has proven useful but it has shortcomings. For example, the open loop approach does not allow for feedback to correct or compensate for inverter non-linearities. It follows that portions of the carrier voltage signal are not useful for providing accurate measurements of the rotor position.
There is a need for an improved technique that takes advantage of known control strategies yet provides more reliable position information. This invention addresses that need.